Alternate Tube Types

Forum to discuss amp circuits besides the 18 Watters and their ilk.

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TriodeLuvr
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Alternate Tube Types

Post by TriodeLuvr »

I'm surprised there aren't any discussions on 18Watt regarding alternate tube types. Numbers like the 5755, 6N2P and 6P3S-E have gained a good rep in hi-fi, and they're much less expensive than the Russian reissues of more traditional tubes like the 12AX7. The 6p14p-ev/EL84M used to be a real bargain too, but prices have increased substantially. I'm not sure they're still worth buying, as opposed to the EL84 label.

The amp I just built uses 12AX7s and EL34s, but my stock of both is almost dry. If I were to build another, I'd use a couple 5755 up front (low microphonics) and 6N2P-EV for the remainder of the gain chain and PI. At the output, I guess $40 or $50 for a pair of EL34 isn't too bad, but it's still possible to buy four 6P3S-E for that price. I have a set of those running in a 40W/ch stereo with almost +500V on the anodes. They're excellent tubes.

All these tubes are plentiful and (for now) inexpensive. They typically last thousands of hours, and carrying a couple spares on the road isn't exactly a hardship. So why isn't there more interest? Is it just a matter of continuing to use what we know? Even the commercial manufacturers seem afraid to offend customers by moving away from traditional types. There's a whole world of really good tubes out there. Considering all the interest in DIY, and the fact we can build whatever we want, it doesn't make sense for everyone to be stuck in such a rut. :)

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Re: Alternate Tube Types

Post by zaphod_phil »

Not stuck in a rut! Most people here are trying to recreate the classic 18W Marshall sound and therefore tend to use the same component types as the original Marshalls.
I'm personally well aware of the good rep some of those other tube types have for Hi-Fi, but as I've said before, This Ain't Hi-Fi! :twisted:
If you've had good success getting the 18W Marshall sound using alternate tube types, please share that and provide sound clips.
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Re: Alternate Tube Types

Post by geoff 1965 »

that's funny you brought this subject up Jack! i very nearly bought these for the lunchbox amp.
s-l1600 (1).jpg
look at the specs of these tubes,shock & vibration resistant,life test of 10,000 hours! i bet you could make a nice little push/pull amp with them.
e80l.pdf
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Re: Alternate Tube Types

Post by TriodeLuvr »

zaphod_phil wrote:
Fri 05/07/21 2:00 pm
Not stuck in a rut! Most people here are trying to recreate the classic 18W Marshall sound and therefore tend to use the same component types as the original Marshalls.
I'm personally well aware of the good rep some of those other tube types have for Hi-Fi, but as I've said before, This Ain't Hi-Fi! :twisted:
If you've had good success getting the 18W Marshall sound using alternate tube types, please share that and provide sound clips.
Seriously - the 18W Marshall sound? Most of the schematics promoted here differ from the originals significantly, and they differ in ways that affect tonal quality much more than building with alternate tube types. That's why I had to build from real Marshall prints located elsewhere. If you think high quality tubes like these aren't useful, that's OK. I was just trying to offer something helpful to those who know how to take advantage of it.

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Re: Alternate Tube Types

Post by TriodeLuvr »

geoff 1965 wrote:
Fri 05/07/21 4:21 pm
that's funny you brought this subject up Jack! i very nearly bought these for the lunchbox amp.
s-l1600 (1).jpg
look at the specs of these tubes,shock & vibration resistant,life test of 10,000 hours! i bet you could make a nice little push/pull amp with them.
e80l.pdf
Many of the "-EV" type Russian tubes are rated like that also. It's roughly the equivalent of the U.S. "WA" suffix. The E80L is a nice tube. There are quite a few American types around that same power level, like the 6AQ5, 6CL6, etc. Any of these can be used to make a killer amp!

Jack
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Re: Alternate Tube Types

Post by Daviedawg »

The 6AQ5 is a great valve with a "softer" output. It can be used in EL84 circuits for a less powerful and more rounded response. But of course it is 7 pin so is not a simple swap. Minor component changes as well for best tone.

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Re: Alternate Tube Types

Post by Bieworm »

TriodeLuvr wrote:
Fri 05/07/21 7:38 pm
zaphod_phil wrote:
Fri 05/07/21 2:00 pm
Not stuck in a rut! Most people here are trying to recreate the classic 18W Marshall sound and therefore tend to use the same component types as the original Marshalls.
I'm personally well aware of the good rep some of those other tube types have for Hi-Fi, but as I've said before, This Ain't Hi-Fi! :twisted:
If you've had good success getting the 18W Marshall sound using alternate tube types, please share that and provide sound clips.
Seriously - the 18W Marshall sound? Most of the schematics promoted here differ from the originals significantly, and they differ in ways that affect tonal quality much more than building with alternate tube types. That's why I had to build from real Marshall prints located elsewhere. If you think high quality tubes like these aren't useful, that's OK. I was just trying to offer something helpful to those who know how to take advantage of it.

Jack
Hey Jack.. do you have some alternative power amp suggestions with a single noval tube so I can try different ones when I build the JTM1 with the 12AU7? Are you pro 2x 6AU6 too, like Phil suggests? He says they're more EL34 vibe thing, which I'm tended to believe. But those are tiny 7 pinners. ..
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Re: Alternate Tube Types

Post by TriodeLuvr »

Bieworm wrote:
Sat 05/08/21 5:14 am

Hey Jack.. do you have some alternative power amp suggestions with a single noval tube so I can try different ones when I build the JTM1 with the 12AU7? Are you pro 2x 6AU6 too, like Phil suggests? He says they're more EL34 vibe thing, which I'm tended to believe. But those are tiny 7 pinners. ..
This is a complex topic. In fact, you're on the edge of the frontier if the goal is to mimic the tone of a 36W Marshall. :lol: The 6AU6 wouldn't be my choice for this. Anode impedance of the EL34 is about 15K - 20K ohms. The 6AU6, like most small-signal pentodes, is closer to 1 megohm. That's problematic, because loading affects tone (harmonic content) and breakup characteristics. It's impossible to load the 6AU6 in the same way as a EL34 or EL84 power pentode. Whether the 6AU6 might sound like an EL34 is anyone's guess, but as you noted, the 7-pin socket limits your options if it doesn't work out. On this point, the 12AU7 can't be easily subbed either, because it's two triodes in a single envelope. Push-pull pentodes will require two sockets. If you think you'll build with the 12AU7 but maybe try pentodes later, you should include an additional socket hole in the chassis at the outset.

Anyway, the issue of loading is almost certainly the reason Marshall chose a triode for the JTM1. The anode resistance of the 12AU7 is a little over 7K ohms, but even that relatively low number required the use of an 18K a-a output transformer. For DIY, there are much better candidates with lower Rp than the 12AU7 (the 7044, 12B4 and 6S4 come to mind). However, the 12AU7 is the only one in current production AFAIK, and commercial manufacturers are limited by that.

If I were to build a flea-power, push-pull pentode amp (1W or less), I would begin by choosing a small power pentode. I'm fond of the 5686, but there are dozens of 9-pin tubes that qualify. Just as example, Rp of the 5686 is about 45K ohms. Loading it with the same 18K transformer used in the JTM1 has a good likelihood of sounding very much like the EL34. The only problem is that the 5686 (like most power pentodes) has greater output power capability than the 12AU7. So, as Phil suggested earlier, I would consider "self-split" mode and the addition of a VVR. I would make sure the preamp had plenty of gain, and also set output biasing to encourage early breakup.

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Re: Alternate Tube Types

Post by geoff 1965 »

what about the 12BH7 that blackstar use push/pull in their little amps?
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Re: Alternate Tube Types

Post by Bieworm »

I agree that technically there are far better options than the 12AU7. But did you see the video of the JTM1 and JMP1 amps? That JTM1 sounds awesome!!! And it sports that 12au7

https://youtu.be/FIQQDHa7qTk
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Re: Alternate Tube Types

Post by TriodeLuvr »

geoff 1965 wrote:
Sat 05/08/21 11:06 am
what about the 12BH7 that blackstar use push/pull in their little amps?
That's also a good choice in a dual triode. Probably not much difference in this service between that and the 12AU7, other than the slightly higher output capability (12BH7).

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Re: Alternate Tube Types

Post by TriodeLuvr »

Bieworm wrote:
Sat 05/08/21 12:27 pm
I agree that technically there are far better options than the 12AU7. But did you see the video of the JTM1 and JMP1 amps? That JTM1 sounds awesome!!! And it sports that 12au7

https://youtu.be/FIQQDHa7qTk
Yes, it sounds excellent in the video. I should apologize for launching into the dual socket scenarios earlier. I totally overlooked the fact you asked about "a single noval tube." Too much information. :lol: Just forget everything I said. :lol: :lol:

You could build it for the 12AU7, then try a 12AV7 later. Allow for the additional 150mA of filament current. The 12AV7 has higher gain, higher Gm and lower Rp than the 12AU7. It's also cheaper. Those are all good things IMO. :)

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